Frequently Asked Questions

Compound interest is interest calculated on both the initial principal and the accumulated interest from previous periods. This means you earn interest on your interest, creating a snowball effect that accelerates growth over time. Read our full guide on what compound interest is.

The calculator uses the standard compound interest formula and produces mathematically precise results for the inputs provided. However, real-world returns may vary due to fluctuating interest rates, fees, taxes, and market conditions. Results should be treated as estimates for planning purposes.

Yes. All calculations happen entirely in your browser using JavaScript. No personal data, financial details, or calculation results are sent to any server. If you use the save feature, your inputs are stored in your browser's localStorage only.

No. This calculator provides estimates for informational and educational purposes only. It does not constitute professional financial advice. Always consult a qualified financial adviser before making investment, savings, or borrowing decisions.

We review and update the calculator, reference rates, and all guide content regularly to ensure accuracy. The current version reflects rates and thresholds for 2025. Check each page's 'Last updated' date for the most recent revision.

Yes. After calculating your results, click the 'Export PDF' button to download a print-friendly PDF containing your input summary, results breakdown, and year-by-year table. The PDF excludes ads and includes a timestamp.

The calculator supports daily (365 times per year), weekly (52), monthly (12), quarterly (4), semi-annually (2), and annually (1). See our compounding frequency comparison for details on how each option affects returns.

Simple interest is calculated only on the original principal, while compound interest is calculated on the principal plus accumulated interest. Over time, compound interest always produces higher returns for savers (and higher costs for borrowers). See our detailed comparison.

The calculator shows gross returns before taxes and fees. In the UK, the Personal Savings Allowance lets basic-rate taxpayers earn up to £1,000 in interest tax-free. ISA interest is entirely tax-free. For accurate after-tax projections, consult a financial adviser.

Please use our contact form and select 'Report a bug or error' from the subject dropdown. We take accuracy seriously and will investigate all reports promptly.

Yes, the compound interest formula works the same way for debt. Enter your loan balance as the principal and the loan's interest rate. Keep in mind that loan repayments reduce the principal, which this calculator doesn't model directly. For a worked example, see our student loan scenario.

AER (Annual Equivalent Rate) is the standardised rate that includes the effect of compounding, showing the true annual return. When comparing savings accounts with different compounding frequencies, always compare the AER rather than the nominal rate.